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EDGAR NELSON TRANSEAU 



from 0°F. in eastern Virginia to — 10°F. in eastern Massachusetts. 

 But these are gradually changing factors and their influence is 

 selective, i.e., they determine which species shall drop out. To 

 account for the sudden disappearance of a large number of species 

 we must look to the discontinuity of the habitats. 



Of the 298 species of southeastern Virginia (fig. 2) , 94 fail to cross 

 Chesapeake Bay. At Delaware Bay the list is decreased to 179 by 

 the loss of 25 species. In central New Jersey 15 drop out. At 



Fig. 2. Diagram showing effect of barriers on the northward extension of the 

 range of 298 coastal plain species found in southeastern Virginia. 



New York harbor the remaining group of 164 species is diminished 

 by 45. Twenty-seven species reach their northern limit on Long 

 Island, and of the 92 which reach Massachusetts 55 go no farther. 

 This leaves 37 to find their "farthest north" along the coast of 

 ]\Iaine and the maritime provinces of Canada. 



The arrangement of the coastal plain plants according to their 

 northern-most stations brings out clearly the fact that the greatest 



